1. Field of the Invention
The present invention relates to an engine mount that is installed between a power unit and vehicle body to provide vibration isolating support of the power unit against the vehicle body, and more particular to an engine mount with a novel structure comprising a stopper mechanism to limit an amount of relative displacement of the power unit against the vehicle body in a cushion-wise fashion.
2. Description of the Related Art
A plurality of engine mounts have conventionally been installed between automobile vehicle bodies and their power units to allow the power units to be supported in a vibration-damping fashion relative to the vehicle bodies. Such engine mounts are generally composed of an upper mounting fixture and a lower mounting fixture which are disposed apart from each other and joined by a rubber elastic body. As disclosed in JP-A-7-89356, for example, they are set up at the bottom on either side of the torque roll axis of the power unit to support the power unit from below on both sides in the lateral direction.
The spring properties of the engine mounts should be relaxed enough to achieve good vibration damping when such engine mounts are used for the vibration-damping support mechanisms for power units in relation to vehicle bodies. However, it is necessary to control significant displacement of the power unit relative to the vehicle body in instances of substantial vibration load. A stopper mechanism for cushioning relative displacement has thus often been provided on the upper and lower mounting fixtures attached to either the vehicle body or power unit in conventional engine mounts.
Such stopper mechanisms are generally constructed by forming contact protrusions that protrude outward from the upper and lower mounting fixtures toward each other, with the contact protrusions disposed apart at a certain interval in the vibration input direction on either side of cushioning rubber.
However, the pair of engine mounts mounted so as to support the power unit at an incline from below on either side of the axis as described above have suffered from the following avoidable problem. Namely, because of the required power unit support properties, as noted in the aforesaid JP-A-7-89356, the mount center axis, which is the elastic main axis extending in the direction in which the upper and lower mounting fixtures face each other, is tilted upward on the inside of the power unit. Therefore, the point of contact at the contact protrusions forming the stopper mechanism is considerably outside the horizontal direction from the upper or lower mounting fixtures.
That is, when the stopper mechanism is formed by the protruding formation of the contact protrusions slanting inwardly from the upper and lower mounting fixtures as indicated in FIGS. 5 and 6 of JP-A-7-89356, the result is a greater distance in the horizontal direction from the point where the lower mounting fixture is fixed to the vehicle body to the point of contact of the contact protrusions. When vertical stopper load is exerted on the contact protrusions, substantial moment acts on the point where the lower mounting fixture is fixed to the vehicle body, making it difficult to obtain satisfactory strength or withstand load capability. When, on the other hand, the stopper is formed by the protruding formation of contact protrusions slanting outwardly from the upper and lower mounting fixtures as indicated in FIGS. 1 and 2 in JP-A-7-89356, the result is a greater distance in the horizontal direction from the point where the upper mounting fixture is fixed to the power unit to the point of contact of the contact protrusions. When vertical stopper load is exerted on the contact protrusions, substantial moment acts on the point where the upper mounting fixture is fixed to the power unit, making it difficult to obtain satisfactory strength or withstand load capability.
In the stopper mechanism for the power unit shown in either FIGS. 1 and 2 or 5 and 6 in JP-A-7-89356, the contact protrusion of the upper mounting fixture that is fixed to the power unit is in the shape of a large pocket which not only is wrapped around so that the contact protrusion on the lower mounting fixture is encompassed outwardly from below, but the walls are integrally formed on both the left and right sides. The resulting increase in the mass of the upper mounting fixture results in a lower natural frequency, with the risk of worsening vibration as a result of resonance in the upper mounting fixture in the low frequency range which tends to cause problems in preventing vehicle vibration.